I am quite experienced with Diphenhydramine, what are you looking for in this drug?
It's not for most people; it can be extremely unpleasant and stressful if unprepared. Black out risk is quite high, I find a small dose of sudafed (the kind that is pseudophedrine, not phenylephrine) helps me to remember my trip. ususally 1/10 pill ratio, suda to dph. (if the dph is 25mg/pill and the sudafed is indeed the sudafed brand)
Stay well hydrated, and it is best to have a tripsitter. I have had many close calls, including my father finding me sitting in the right lane of a local highway, convinced I was at poker night at my friends house. This drug follows no rules, and does as it pleases.
Extracting it would not go well for a lot of reasons i'd think, the only one I'd care to point out is, many times the come up is very sudden, and in a more pure form I can't imagine it being any more forgiving. I find myself going from stone sober to mindfuck before I know it, only realizing the trip is under way after returning from microsleep.